In a large bowl, mix flour, salt, and sugar. Cut in the butter with a pastry cutter or your fingers until crumbly.
Add ice water a tablespoon at a time, mixing gently until the dough comes together. Divide in half, shape into disks, wrap, and chill for 1 hour.
Preheat your oven to 400°F (200°C).
Roll out one disk on a floured surface and fit it into a 9-inch pie dish. Refrigerate while you prepare the filling.
In a bowl, combine blueberries, sugar, cornstarch, lemon juice, and cinnamon. Stir gently to coat the berries.
Pour the filling into the chilled pie crust. Roll out the second disk and lay it over the top, or cut into strips for a lattice. Trim and crimp edges.
Whisk the egg and milk. Brush over the crust.
Place pie on a baking sheet and bake for 45 to 50 minutes, until the crust is golden and the filling is bubbling.
Cool at room temperature before slicing. (I know, the wait is torture!)